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Chemistry OCR A-Level > Topic 4 > Flashcards

Topic 4 Flashcards

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1
Q

alkenes are which kind of hydrocarbons

A

unsaturated

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2
Q

what is the general formula for alkenes

A

CnH2n

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3
Q

what prohibits rotation in alkenes

A

the pi bond
it locks the 2 carbon atoms into position

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4
Q

what is the shape around the carbon atoms in the double bond and why

A

120 degree bond angle
repel each other equally
in the same plane
trigonal planar
3 regions of electron density

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5
Q

what is stereoisomerism

A

same structural formula but a different arrangement of atoms in space

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6
Q

what are the 2 types of stereoisomerism

A

E/Z isomerism
Optical isomerism

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7
Q

when is cis/trans isomerism applicable

A

when molecules has C=C double bonds
Each carbon atom in double bond is attached to 2 different groups

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8
Q

what is the cis isomer

A

hydrogen atoms on each carbon are on the same side

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9
Q

what is the trans isomer

A

hydrogen atoms are diagonally opposite each other

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10
Q

what are the Cahn-Ingold Prelog rules for deciding E/Z isomerism

A

higher atomic number = higher priority
groups of higher priority on the same side of the double bond of the Z isomer

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11
Q

describe hydrogenation of alkenes

A

an alkene is mixed with hydrogen and passed over a nickel catalyst at 423K forming an alkane

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12
Q

describe halogenation of alkenes

A

Rapid addition reaction between an alkene and Cl/Br at room temperature to form a halogenalkane

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13
Q

how do you test for alkenes

A

orange bromine water turns clear

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14
Q

describe hydration of alkenes

A

an alkene is reacted with steam in the presence of a phosphoric acid catalyst, forming an alcohol
2 products can be formed

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15
Q

what is the mechanism for addition reaction

A

electrophilic addition

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16
Q

outline an electrophilic addition reaction between an alkene and hydrogen bromide

A

H-Br is a polar molecule
electron pair in a pi bond is attracted to it
double bond breaks
bonds forms H and C atoms
H-Br bond breaks by heterolytic fission
bromide ion and carbocation formed
Br- reacts with carbocation

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17
Q

how does electrophilic addition take place with molecules with molecules that are non-polar

A

when the molecule approaches the pi bond, the electrons in the bond are repelled and this induces polarity

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18
Q

what is the Markownikoff’s rule

A

In electrophilic addition, when the carbocation is formed, it can be primary, secondary, tertiary.
Tertiary is the most stable so is the most likely product

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19
Q

what is carbocation

A

positively charged molecule of carbon

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20
Q

why is tertiary carbocation the most stable

A

connecting alkyl groups donate and push electrons towards the positive charge of the carbocation
therefore more alkyl groups = a more stable ions

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21
Q

what is the name of the reaction for a polymer’s formation from alkenes

A

addition polymer

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22
Q

how is the monomer unit displayed

A

displayed formula with an (n) before it to signify many units

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23
Q

how is the repeat unit of the polymer are displayed

A

displayed formula, in square brackets, an (n) is placed after to signify a large number of repeats

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24
Q

what are the conditions for a polymerisation reaction

A

high temperature and pressure

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25
Q

what are the uses of polypropene

A

Toys, packing crates, guttering, rope fibre

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26
Q

what are the uses of polyphenylethene - polystyrene

A

packaging materials
food trays + cups

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27
Q

what are the uses of polytetra fluroethene

A

coating for non-stick pans
permeable membrane for clothing
cable insulation

28
Q

downside of current disposal of waste of polymers?

A

very unreactive
non-biodegradable with serious environmental effects

29
Q

what are the benefits of recycling polymers

A

reduces environmental impacts by conserving fossil fuels and decreasing waste

30
Q

how is a double bond formed

A

3 sigma bonds formed
1 electron left in a p-orbital
a pi bond forms from the sideways overlap of 2 p-orbitals

31
Q

what is an elimination reaction

A

the removal of a small molecule from a larger one

32
Q

what is the functional group and suffix for
an alkene
alcohols
aldehyde
ketones
carboxylic acids

A

c=c -ene
OH -ol
-CHO -al
C(CO)C -one
COOH -oic acid

33
Q

functional group and prefix for haloalkane

A

-Cl/-Br/-I
Chloro-
Bromo-
Iodo-

34
Q

what is the difference between a saturated and unsaturated hydrocarbon

A

saturated = only single bonds
unsaturated = mutiple bonds

35
Q

what is a homologous series

A

family of compounds with similar chemical properties differing by the addition of a group

36
Q

what is a functional group

A

part of the organic molecule that is responsible for the molecules chemical properties

37
Q

what is an aliphatic hydrocarbon

A

carbon atoms are joined to each other in a straight chain

38
Q

what is an alicyclic hydrocarbon

A

carbon atoms are joined to each other in a ring (cyclic) structure

39
Q

what is an aromatic hydrocarbon

A

some/all carbon atoms are found in a benzene rings

40
Q

what is the difference between alkanes, alkenes and alkynes

A

ane - single C-C bonds

ene - one+ C=C double bond

yne - 1+ C-C triple bond

41
Q

what is a general formula

A

simplest algebraic formula for any member of a homologous series

42
Q

what is displayed formula

A

shows relative positioning of all of the atoms in a molecule + the bonds

43
Q

what is the structural formula

A

shows which groups are bonded together
CH3CH2CH3

44
Q

hwo is skeletal formula formed

A

remove all of the carbon and hydrogen labels from the carbon chain
remove any bonds to hydrogen atoms

45
Q

how does skeletal formula work

A

one line = a single bond
intersection of 2 lines = a carbon atom
end of a line = -CH3 group

46
Q

what is a structural isomer

A

compounds with the same molecular formula but different structural formula

47
Q

what is homolytic fission and what is formed after

A

when a covalent bond breaks, each of the bonded atoms takes 1 electron from the shared pair
2 atoms with an unpaired electron - radicals

48
Q

what is heterolytic fission and what is formed after

A

whena covalent bond breaks, 1 bonded atom takes both of the electrons fro the shared pair
a positive ion ad a negative ion

49
Q

what are curly arrows used to show

A

movement of electron pairs when bonds are broken or made

50
Q

what is an addition reaction

A

2 reactants form 1 product after being joined together

51
Q

what is a substitution reaction

A

an atom/group of atoms is replaced by a different atoms/group ofatoms

52
Q

what is the main use of alkanes

A

fuel

53
Q

what is the general formula of alkanes

A

CnH2n+2

54
Q

what kind of covalent bonds are formed in alkanes

A

sigma bonds

55
Q

what is a sigma bond

A

the overlap of 2 orbitals

56
Q

how are alkanes separated

A

fractional distillation

57
Q

how does chain length affect bp and why

A

longer chain length raises boiling point as there is a greater surface area of contact which means stronger London forces which require more energy to overcome

58
Q

what is the effect of branching on bp and why

A

lowers boiling point as there is less surface area of contact which means weaker London forces which require less energy to overcome

59
Q

why are alkanes fairly unreactive

A

C-C, C-H sigma bonds are strong
C-C bonds are non polar
Similar electronegativity of carbon and hydrogen

60
Q

what is complete combustion and what are the products

A

alkanes burn completely to produce CO2 and H2O

61
Q

what are the 2 products from incomplete combustion of alkanes

A

carbon monoxide and water

62
Q

name the mechanism for bromination of alkanes

A

free radical substitution

63
Q

what are the 3 stages of free radical substitution

A

initiation
propagation
substitution

64
Q

describe initiation of free radical substitution

A

covalent bond in a bromine molecule is broken by homolytic fission
energy is provided by UV radiation
Br-Br -> *Br + *Br

65
Q

describe propagation stage of free radical substitution

A

CH4 + Br* –> CH3 + HBR
CH3 + Br2 –> CH3BR + Br*

66
Q

describe termination stage of free radical substitution

A

2 radicals collide forming a molecule with all electrons paired
1. Br* + Br* –> Br2
2. *CH3 + *CH3 –> C2H6
3. CH3 + Br –> CH3Br

67
Q

what can occur after a radical substitution reaction

A

further substitution

Chemistry OCR A-Level (2 decks)

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